Astronaut Scott Kelly has announced that he will be leaving NASA on April 1, 2016. Photo Credit: NASA

Astronaut and retired U.S. Navy Captain Scott Kelly announced his retirement from NASA yesterday, via Facebook. In a letter entitled “A thousand miles begins with a single step,” Kelly explains that he remains “ever committed and dedicated to the service of human exploration and advancement in space or on Earth,” and that his departure from NASA, effective April 1, symbolizes the next step in his own journey.

Having received his naval commission from the State University of New York Maritime College in May 1987, with nearly 20 medals and commendations from the U.S. Navy and NASA, Kellyhas had an extensive career. Including his most recent mission aboard the International Space Station, Kelly has logged more than 520 days in space – holding the record for time spent in orbit by a U.S. Astronaut.

Following his graduation from the U.S. Naval Test Pilot School in June 1994, Kelly has logged more than 8,000 hours in more than 40 different aircraft and was the first pilot to fly an F-14 with a digital flight control system.

His first flight as a NASA astronaut was aboard Space Shuttle Discovery on STS-103, and it brought him to the Hubble Space Telescope (HST) for enhancement upgrades. During this 8-day mission, which lasted from December 19 through December 27, 1999, three separate spacewalks (EVAs) were performed by Kelly’s crewmates to repair a number of malfunctioning stabilization gyros, which had caused Hubble to enter a state of dormancy while it awaited maintenance.

Commanding STS-118 aboard Endeavour, Kelly’s second spaceflight would bring him to the International Space Station (ISS) for the first time. Delivering the station’s third starboard truss segment, STS-118’s mission lasted 12 days.

His first extended tour aboard the orbiting lab came during his third mission. Launched aboard the Soyuz TMA-M spacecraft in October of 2010, Kelly commanded ISS Expedition 26 for 159 days before returning to Earth on March 16, 2011.

Kelly’s final and perhaps most notable mission came to a close on March 1 of this year. Serving first as Flight Engineer for Expeditions 43 and 44, and then as Station Commander for 45 and 46, Kelly – along with Russian Cosmonaut Mikhail Kornienko – spent 340 days on the ISS, and completed nearly 400 experiments in an effort to better understand the affects of long-term spaceflight on the human body.

Retired astronaut Mark Kelly, Scott Kelly’s twin, remained on Earth during his brother’s missionto serve as an exact genetic basis for comparison upon Scott’s return. In his letter, Scott Kelly emphasizes his continued commitment “to participate in the ongoing research related to NASA’s one-year mission for as long as is necessary.”

Before ever launching into space, Kelly’s time at NASA began in April 1996, where he worked as part of the Astronaut Office Spacecraft Systems/Operations branch. Furthermore, following his return from STS-103, Kelly served as NASA’s Director of Operations in Star City, Russia.

Though his days spent in orbit of the Earth are now behind him, Kelly is looking forward to continuing his 30 years of public service in a “new role”. What that role may be is yet to be determined, but as Kelly states in the end of his letter, “To continue toward any journey, we must always challenge ourselves to take the next step.”

AS the commander of Expedition 45, Kelly carried out his first extra-vehicular activity on Oct. 28, 2015. Photo Credit: NASA

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